In vehicle control systems, control functions of an entire vehicle are distributed. Control devices are provided for the respective distributed control functions, and adjustments between the distributed control functions are made in such a manner that they communicate with each other via an intra-vehicle communication network (for example, tta Group, “TTA-Group Forum,” [online], Internet URL: http://www.ttpforum.org/, search date: Nov. 19, 2002).
Exemplary communication protocols that are used in vehicle control systems that perform distributed processing of the above kind are TTP/C of the TTP consortium in Europe (JP-A-2000-268288) and FlexRay of the FlexRay consortium (Flex-Ray-Consortium, FlexRay, [online], Internet URL: http://www.flexray-group.org/, search date: Nov. 19, 2002). These are communication protocols based on TDMA (time division multiple access). TDMA realizes multiple access in such a manner that time slots that are separated from each other by a constant time interval are occupied by data of different communications.
In vehicle control systems using TDMA, time slots are assigned in advance to respective ECUs as control devices and each ECU can send data to an intra-vehicle communication network using only the time slot assigned thereto. The assigned time slots have a periodic structure and hence it is not the case that each ECU can send data at any time.
If a vehicle control system that performs distributed processing of the above kind is configured in such a manner that an ECU for controlling an engine ignition device, a fuel injection device, and electromagnetic valves and an ECU for detecting the rotation of a crankshaft are distributed and signal exchange between those ECUs is performed via an intra-vehicle communication network, various advantages are obtained. For example, the configuration is made simpler than in conventional engine control systems.
However, in such a vehicle control system, if, for example, TDMA is employed in the above manner, problems occur in the controls on the fuel injection device, the ignition device, the electromagnetic valves, etc. that are performed in synchronism with the crankshaft rotation of an engine. In general, the crankshaft rotation is detected by using a crankshaft signal that is output from a crankshaft sensor. The crankshaft signal is such that the signal level is alternately switched between a high level and a low level every time the crankshaft rotates an interval of a prescribed value (e.g., 2.5°). Consideration will be given below to a sensor ECU that sends information indicating the switching between the high level and the low level to the intra-vehicle communication network on the basis of the crankshaft signal is supplied from the crankshaft sensor.
FIG. 12 shows a time relationship between the crankshaft signal and information that relates to the crankshaft signal and is sent to the intra-vehicle communication network. In FIG. 12, the solid line in the top part and the rectangles in the bottom part represent the level of the crankshaft signal and an arrangement of transmission time slots that are assigned to the ECUs, respectively. Time slots 101, 102, and 103 that are represented by hatched rectangles in the bottom part are assigned to transmission from the sensor ECU.
Information indicating switching to the high level of the crankshaft signal and corresponding to 0° CA (crankshaft angle) that corresponds to a TDC (top dead center point) of the crankshaft is sent from the sensor ECU by using the time slot 101 that occurs immediately after the switching. Information indicating switching to the low level of the crankshaft signal and corresponding to 2.5° CA (crankshaft angle) is sent by using the time slot 102. Then, information indicating switching to the high level and corresponding to 5° CA (crankshaft angle) is sent by using the time slot 103. Other ECUs that receive the crankshaft signal switching information that is sent in the above manner can recognize the crankshaft angle by counting the number of received pieces of information.
However, as shown in FIG. 12, where the time slots are not synchronized with the crankshaft rotation, temporal deviations occur between the crankshaft rotation and the pieces of information relating to the crankshaft rotation that are actually sent to the intra-vehicle communication network.
Further, the crankshaft rotation speed varies depending on engine rotation speed, which means that the period of the crankshaft signal varies depending on engine rotation speed. FIG. 13 shows a relationship between the crankshaft signal and the time slots in a case that the engine rotation speed is higher than in the case of FIG. 12.
In this cases the level of the crankshaft signal varies three times (i.e., to low, high, and low) from an instant when information indicating switching to the high level is sent by using a time slot 104 to an instant when the next assigned time slot 105 arrives. However, the sensor ECU merely sends, to the network, by using the time slot 105, information indicating switching to the low level that occurs immediately before, reception-side ECUs cannot receive two pieces of information indicating switching of the crankshaft signal. As a result, the reception-side ECUs recognize that a value that is deviated from the true crankshaft angle by 5° is a current crankshaft angle. If this situation continues, the deviation increases and the deviation between the control timing and the crankshaft angle also increases. This results in a problem that in terms of the relationship between the engine ignition and the fuel injection processing neither a high engine power nor a low degree of emission can be obtained.
Similar problems may occur even in the case that TDMA is not employed as a communication method of the intra-vehicle communication network. That is, problems occur when because of a low network communication rate the next and even the second next crankshaft signal switching timing arrives before the sensor ECU completes outputting information indicating switching of the crankshaft signal to the network.